Achieving high-efficiency perovskite solar cells (PSCs) typically necessitates postdeposition annealing under stringent environmental controls, such as low relative humidity or inert atmospheres. These demanding conditions significantly increase the complexity and cost of device fabrication. Therefore, developing an annealing strategy for obtaining high-quality, phase-pure α-FAPbI3 perovskite in ambient or high-humidity environments is critically important. Here, we demonstrate that coevaporated FAPbI3 perovskite active layers annealed in a saturated-humid environment exhibit pure α-phase and thus markedly superior device performance compared to those annealed in normal air or an inert atmosphere. The resulting preferred crystal orientation, superior carrier transport properties, and retarded charge carrier recombination collectively enable an excellent power conversion efficiency (PCE) of up to 21.3% in vacuum-deposited inverted PSCs. Additionally, these devices also deliver excellent performance under indoor environmental light-harvesting, achieving PCEs of 34.9% and 36.7% under 1000 lx illumination from 6500 K and 3000 K fluorescent light sources, respectively.
Jheng et al. (2026) studied this question.